Content protection may be cryptographically based or signal-processing based or a combination thereof. Generally, cryptographically-based content protection is applied to the digital domain, while signal-processing based content protection is applied to the analog domain.
There are many examples of cryptographically-based content protection in use today. Digital video discs (“DVDs”) use a Content Scrambling System (“CSS”) that requires a 40-bit long key to decipher the encrypted content. Content Protection for Recordable Media (“CPRM”) is a broadcast encryption technology applied to physical media, where a media key block is prerecorded on blank media. Content Protection for Pre-recorded Media, a variant of CPRM, is used to protect DVD Audio formatted discs. CPRM is also used to protect content stored in Secure Digital Memory Cards, Secure CompactFlash, the IBM MicroDrive, and DVD video recorders.
More recent developments include Digital Transmission Content Protection (“DTCP”), a public-key technology applied to a digital bus, such as a Universal Serial Bus (“USB”) and an Institute of Electronic and Electrical Engineers (“IEEE”) 1394 bus (“Firewire”). High Definition Content Protection (“HDCP”) has been proposed to protect content transferred from a Digital Video Interface (“DVI”) (a digital video interface to a high-definition monitor/television). HDCP expands on authentication of DTCP to establish a session key used to encrypt video data.
In the software arena, content protection includes cryptographic switching (“cryptoswitch”) and digital signets technologies. Cryptoswitch involves only having a small portion of a program in the clear for runtime, and leaving the remainder encrypted. Signets are used to detect unauthorized modification of a program.
The standards bodies of Digital Video Broadcast and TV Anytime have considered proposals for content protection in home networks, such as SmartRight, Open Conditional Content Access Management (“OCCAM”) and xCP Cluster Protocol. Other network or system level approaches include Broadcast Flag, Content Protection System Architecture (“CPSA”) and Digital-Rights Management (“DRM”) systems. In Broadcast Flag, a bit is set to indicate content is not to be distributed over the Internet, and otherwise the content is protected by DTCP and CPRM. CPSA is another architecture describing how, DTCP and CPRM fit together along with watermarking, using interlocking licenses. DRM systems use the Internet to distribute keys for decryption through a clearing house.
In the signal-processing based content protection arena, an out-of-specification television signal, not detectible by a television, but detectable by most video recorders is used. Also, digital watermarking for copy control, whether record control or playback control, is used. Pattern recognition (“fingerprinting”) is being considered. However, recognition is a statistical process, which by definition, is inexact. A library of content needing to be interrogated would be significantly large, for example for broadcast monitoring. Accordingly, watermarking is presently more favored for identification purposes.
Because of the many ways that content may be copied, displayed and distributed, no one technology is a complete solution to protecting content within all of these possible contexts. Accordingly, technology that advances the interests of a content protection environment is desirable and useful.